Cross-linked, closed-cell, foams formed from polyurethane (PU), ethylenevinyl acetate (EVA), or EVA/ethylene-alpha-olefin copolymer blends are commonly used for midsoles in footwear applications. The function of the midsole is mainly cushioning, which helps to distribute, and soften, the force of impact when feet hit the ground. However, the dynamic properties of PU- and EVA-based foams change with temperature. These foams become too hard during cold weather, which results in less cushioning effects. There is a need for new foam compositions that provide consistent dynamic properties (for example, constant storage modulus (E′)) over a broad range of temperature, as compared to incumbent EVA- and PU-based foams.
International Publication WO 2011/079207 discloses a composition comprising at least the following: A) an ethylene/α-olefin/polyene interpolymer, B) an ethylene/α-olefin copolymer, C) optionally at least one filler, D) at least one crosslinking agent, and E) at least one blowing agent. The absolute difference in the solubility parameters between the polymer components is less than, or equal to, 0.15 (cal/cm3)1/2.
U.S. Publication 2006/0211819 discloses polymer blends comprises the following: 1) at least one ethylene/α-olefin interpolymer and 2) at least one polyolefin, or at least one styrenic block copolymer, or a combination thereof. Such polyolefins include, but are not limited to, high melt strength, high density polyethylene, and high melt strength polypropylene. The ethylene/α-olefin interpolymers are random block copolymers, comprising at least a hard block and at least a soft block. The polyolefins can be homopolymers or interpolymers.
U.S. Publication 2008/0207786 discloses an ethylene-propylene-diene rubber foamed material, obtained by foaming a rubber composition containing an ethylene-propylene-diene rubber, a quinoid cross-linking agent, and an organic peroxide cross-linking agent.
U.S. Publication 2006/0199872 discloses foamable compositions and foams, comprising at least an ethylene/α-olefin interpolymer. The foam has a density from greater than 150 to about 500 kg/m3. The foamable compositions further comprise a blowing agent and a crosslinking agent. The ethylene/α-olefin interpolymer is a multi-block copolymer comprising at least one soft block and at least one hard block.
U.S. Publication 2006/0199911 discloses a polymer composition comprising at least an ethylene/α-olefin interpolymer and at least one other polymer. The other polymer can be selected from a second ethylene/α-olefin interpolymer, an elastomer, a polyolefin, a polar polymer, and an ethylene/carboxylic acid interpolymer or ionomer thereof. The ethylene/α-olefin interpolymer is a block copolymer having at least a hard block and at least a soft block.
Additional polymer formulations are disclosed in the following references; U.S. Pat. Nos. 5,288,762, 6,221,964, 6,325,956, 6,340,717, 6,384,096, 6,767,931, 7,557,147; U.S. Publications 2004/0039075, 2004/0142405; International Publications WO 2011/163176, and WO 2010/040019.
However, as discussed above, there remains a need for new foam compositions that provide consistent dynamic properties (for example, constant storage modulus (E′)) over a broad range of temperature, as compared to incumbent EVA- and PU-based foams. These needs have been met by the following invention.